Conventionally, as roller bearings for ratably supporting the wheels of a heavy vehicle on the suspension system thereof, taper roller bearings having a large load capacity and high rigidity have been used favorably. In this kind of taper roller bearing, the outer ring is usually press-fitted into a housing with an interference and secured thereto, and the inner ring is secured to a shaft member with a very small clearance or an interference to prevent relative rotation therebetween; however, a creep phenomenon may occur in which the relative rotation therebetween is caused, for example, due to the change in load associated with the movement of the rolling elements. In particular, in a roller bearing being used under an outer-ring rotation load condition, in the case that the roller bearing is used under a heavy load condition in which P/C (P: bearing load, C: basic dynamic load rating) is more than 0.13, a creep phenomenon may occur at the inner ring serving as a stationary ring. This creep phenomenon may occur not only in taper roller bearings, but also in cylindrical roller bearings and spherical roller bearings being used under outer-ring rotation load conditions, such as in planetary gears for general industrial machinery.
While studying the creep phenomenon, the present inventors have found that the creep phenomenon is caused by the fact that when a heavy load is applied to a bearing, loads on the rolling elements thereof are increased, and local expansion and contraction on the surface of the inner ring raceway are increased at the time when the rolling elements pass.
More specifically, in the case that one point in the loaded area on the surface of the inner ring raceway is viewed, in a state in which a rolling element is placed on the surface of the inner ring raceway, the inner ring contracts in the radial direction and expands in the circumferential direction due to the load on the rolling element, and after the rolling element has passed, the inner ring returns to its original shape. Hence, each time each rolling element passes, the inner ring repeatedly expands and contracts in the circumferential direction, thereby causing a creep phenomenon in which the inner ring rotates with respect to the shaft. If this creep phenomenon is generated, wear occurs on the surface of the shaft, and abrasion powder on the surface gets into the bearing, thereby causing premature flaking.
It is conceivable to increase the interference of the shaft to suppress the creep phenomenon under the heavy load condition.
Furthermore, in the rolling element described in Patent Document 1, on the surface to be fitted on a mating member, a relief groove is formed in the stationary ring within a range not exceeding the width of the groove on the raceway surface. With this configuration, even if the raceway of the bearing is deformed elastically due to the passing of the rolling element, the elastic deformation is not transmitted to the mating member because the stationary ring is not made contact with the mating member, whereby the creep phenomenon can be suppressed.
Moreover, in the roller bearing described in Patent Document 2, the creep phenomenon is prevented by increasing the thicknesses of the inner ring and the outer ring.